This invention relates to hand operated power tools of the type for reciprocating saw blades and the like. Such tools are electrically operated and characterized by a driving head that reciprocates a ram rod to which a saw blade or the like is attached as by means of a set screw or chuck. A feature of these power saw tools is a shoe that slidably engages and limits the penetration of the saw blade into said work. A heavy duty power saw tool of the type under consideration is shown in FIG. 1 of the drawings herein, with the aforesaid guide shoe removed and replaced by the file adapter of the present invention. Also, a common hand file (modified) replaces a saw blade for which this particular power tool is designed.
Heretofore, slender elongated saw blades of thin cross section (0.040" to 0.050"), and sander attachments, have been operated by such power tools, so as to reciprocate against and through work pieces, and various guide mechanisms have been associated with the controlling shoe to back up the saw blade as it is pressed against said work piece. And a characteristic of these power saw tools is the relatively short stroke of the saw blade which too is relatively short and not lengthy as a hand saw would be. In other words, the power tools of the prior art have not been conducive to the adaption thereto of lengthy hand files.
It is the common hand file with which this invention is particularly concerned, and it is to be understood that there are various special files to which the adapter system of the present invention is to be applied. The files with which this invention is concerned are elongated bars with a surface upon which teeth are formed to engage and cut material from a work piece. The cross sectional configuration of said bars varies in order to present a toothed surface, and the coarseness and number of teeth is as circumstances require. For example, files can be flat, round, half-round, triangular or rectangular, and the tooth configuration coarse cut, bastard cut, single cut, double cut etc. There are also rasp files with an arrangement of round cupped teeth. It is to be understood therefore that this invention relates to all files, a characteristic of which is a body of hardened steel having a base end with an annealed tang of tapered configuration extending from a base end thereof. A full sized common file has an active toothed face nine inches long and seven eights inches wide, with a base and tang approximately three inches long extending therefrom (these dimensions are variable). It is this common hand file with which this invention is particularly concerned, it being an object of this invention to modify such a file and thereby adapt it to a chuck of a power saw tool.
Hand filing involves manipulative skills. That is, the teeth are formed so as to cut only during a forward pushing motion during which downard pressure against the workpiece must be applied. Too little pressure especially on hard materials tends to dull the teeth quickly. And too much pressure tends to clog the teeth and break them off. Accordingly, pressure against the workpiece must be applied in order to render a file effective, and it is to this end that it is an object of this invention to provide a power saw tool adapter for applying work pressure to the back side of a file chucked in said tool. In accordance with this invention, said work pressure is applied to the base-tang end portion of the file, said work pressure being shared by the chuck and ram-rod of the power tool.
In the coarse of rough shaping a work piece with the power saw tool file adapter herein disclosed, lateral pressures are applied to the file that is anchored to the reciprocating chuck of the tool. In practice, the active toothed portion of the file extends four or five times its base length forming a lever arm that could be destructive of the coupled attachment of the file to the tool chuck. Therefore, it is an object of this invention to eliminate bending stress from the file to chuck connection, by means of a fixedly positioned guide roller operating as a resistance member in a guideway formed in the back side of the file base.
A feature of this invention is the file adapter that replaces the prior art shoe of power saw tools, thereby providing 1) a resistance for the application of downward work pressure, and 2) a double resistance for side to side reception to lateral work pressures; all of which prevents destructive forces from being applied to the file-to-chuck connection. Accordingly, a second class lever is involved in any situation, the chuck of the power tool being the fulcrum, the guide roller being the resistance, and the extended file being the forceful lever arm.